Self-adjusting brake



SELF-ADJUSTING BRAKE May 29, 1956 Filed Oct. 5, 1951 3 Sheets-Sheet 1Fig.1.

INVENTOR WITNESSES: 5%7X7i/ Gilbert Currie MZBW ATTORN EY May 29, 1956SELF-ADJUSTING BRAKE Filed Oct. 3, 1951 3 Sheets-Sheet 2 h WITNESSES:INVENTOR Gilbert Currie. ffm BY ATTORNEY G. CURRIE 2,747,698

United States Patent SELF-ADJUSTING BRAKE Gilbert Currie, Williamsville,N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application October 3, 1951, SerialNo. 249,497

19 Claims. (Cl. 188-171) This invention relates generally to brakes andis particularly directed to a brake which compensates brake wear,misalignment of parts and requires no adjustment throughout the usefullife of the brake shoes or lining.

In certain of its general aspects this invention is related toapplicants Patent 2,514,378 and to applicants copending application,Serial No. 249,496, filed on the same date as this application andentitled Brake, now Patent No. 2,685,945. In some of its more detailaspects this invention is related to applicants copending application,Serial No. 249,498, filed on the same date as this application andentitled Brake, all the aforesaid items assigned to the assignee of thisinvention.

This invention, in one form of embodiment is illustrated in connectionwith an electric brake of the double block type in which a springapplies the braking torque and a solenoid or electromagnet operatingagainst the spring or braking torque, moves the brake to disengagedposition.

In the usual case, double block brakes comprise a brake wheel and havebrake arms on opposite sides of the brake wheel, which carry the brakeshoes adjacent their extremities. The brake is set by a compressionspring and a link system connecting the free extremities of the brakearms. This forces the brake arms together, and the brake is usuallyreleased by means of a bell crank having its middle fulcrum on the brakearm extremity adjacent the compression spring, and one end thereofattached to the link. Force applied in the proper direction to theremaining extremity of the bell crank, drives the free extremities ofthe brake arms apart and releases the brake. Frequently on double blockbrakes, the bell crank is actuated by a solenoid.

Most brakes of this general type have three adjustments, one for varyingthe torque, and hence, for varying the braking and releasing effort byvarying the amount of spring compression, one for equalizing the shoeclearances, usually by means of separate adjustments on the shoes, andthe third for adjusting the stroke or travel of the solenoid orelectromagnet plunger or armature.

While these adjustments may vary for different types of brakes, they areessentially the same. In the typical case, after the brake is mounted inposition, it is necessary to make most, and usually all of theseadjustments, and the successful operation of the brake depends upon theskill with which the adjustments are made.

These adjustments, under ideal working conditions, ordinarily require afair degree of skill, to obtain the most eflicient operation of thebrake. In many instances, however, brakes are installed inout-of-the-way places where lighting is poor and where the space iscramped. Under these conditions, it is extremely difficult to make thethree adjustments herein above mentioned. In such instances, the brakeis usually always out of adjustment and maximum operating efficiency istherefore not obtained.

Initial adjustments, however, hold only for the thickness of the newbrake shoe lining. As the brake is used and the linings are worn, thebrake is continuously moving 2,747,698 Patented May 29, 1956 out ofadjustment. When the lining has worn an amount equal to the initial shoeclearances, the travel of the armature or solenoid plunger has beendoubled, and it is usually necessary to readjust the brake to restorethe travel to its original amount. If the adjustments are not made atthe proper time, or are not properly made, brake failures evidenced inexcessive heating and burned out solenoid coil-s may result.

Due to the facility of adjustment of the brake of this invention at thetime of manufacture, and due to the fact that this brake automaticallyadjusts itself during operation, it will be appreciated that brakefailures may be minimized with no maintenance time and effort beingrequired other than to replace worn out lining. In accordance withanother feature of this invention, movement of certain specified partsof the brake to given limit positions may be utilized by suitable,visual, or audible indicating means, to signal the operator that thebrake must be relined.

Inaccordance with the foregoing considerations, it is generally oneobject of this invention to provide a brake of the character generallyreferred to, which is simple in its elements with respect to operationalrequirements and consistent in its operation.

It is also a general object of this invention to provide a brake of thecharacter referred to which may be factory adjusted and which requiresno adjustment after it is placed in operation.

Another object of this invention is to provide a brake in whichmisalignment of the brake Wheel with respect to a center line of thebrake assembly is automatically compensated.

Stated otherwise, with regard to the preceding object, it is also anobject of this invention to provide a brake such that factory adjustmentof the brake with the brake wheel in one position is not affected bylocation of the brake wheel in another position with respect to thebrake shoes when the brake is installed, within the limits ofcompensation of the mechanism.

A more specific object of this invention is to provide a brake of theclass generally referred to in which the distance of travel of thesolenoid plunger or electromag net armature in releasing the brake isconstant and is always confined to the same definite path, irrespectiveof wear of the brake lining, or brake wheel misalignment to therebyeliminate overtravel and side pull of the plunger or armature.

The foregoing statements are merely illustrative of the various aims andobjects of this invention. Other objects and advantages will becomeapparent from a study of the following specification, when considered inconjunction with the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a brake assembly embodyingthe features of this invention.

Figure 2 is a bottom view of Figure 1, illustrating certain details ofthe brake linkage.

Figure 3 is an end view of the brake assembly of Figure l, as viewedfrom the right end of the brake, which view illustrates certain otherdetailed features of the brake linkage and general construction, and

Figure 4 is a view taken on section line IV-IV of Figure 3.

The various components of the brake assembly are mounted upon a supportor base section comprising a pair of spaced parallel angles 1. Theseangles are suitably spaced apart to receive therebetween the variouslevers of the brake linkage system. At the right end of the base of thebrake, as viewed in Figures 1 and 2, there are mounted two brake armassemblies, generally designated, 2 and 3. These brake arm assembliescomprise a pair of similar levers, respectively designated 2a and 2b,and 3a and 3b. Brake arm levers 2a and 2b,

are pivotally connected between the vertical flanges of the base anglesby means of a shaft 4, provided with reduced diameter, threaded endsections, which clear through suitably positioned holes in the mentionedvertical flanges of the base section, and which are secured by means ofnuts 5, which thread thereover. Brake arms 3a and 3b are similarlypivotally secured between the vertical flanges of the base angles bymeans of a shaft 6, the ends of which extend through the verticalflanges and have threaded thereover nuts 7.

These brake arm assembly pivot mountings, for the respective brake armassemblies, are arranged in suitably spaced relation along the basesection and as seen in Figure 1, vertical extensions of the brake armsproject upwardly on each side of a brake wheel 3.

Brake shoes 9 and 10 are respectively pivotally connected to the upperextremities of the respective brake arm assemblies 2 and 3 by means ofrespective pivot pins 11 and 12, which extend through respective bosses13 and 14 on the brake shoes and engage the upper ends of the respectivelevers of the brake arm assemblies. As a general rule, sufiicientfrictional restraint in this pivotal mounting of the brake shoes on thebrake arms is provided so that the shoes do not rotate due to their ownweight, whenever the brake arms are moved to brake released position.The brake shoes are properly aligned by movement of the brake arms to aposition in which the brake shoes engage the wheel. The frictionalrestraint is overcome due to the force of this engagement and the brakeshoes are properly oriented with respect to the wheel, and maintain thisposition in the brake released position.

A lever assembly generally designated 15, is connected to each brake armassembly at a point on each assembly which is displaced from therespective points of pivoting of the brake arm assemblies on the base.The point of connection of lever assembly 15, with brake arm assembly 2is designated 16, which is represented in a pin extending through bothsections 15a and 15b of lever 15,

and terminating in the respective levers 2a and 2b of brake arm assembly2. A pin 17, which extends through, and is secured in both leversections 15:: and 15b of the lever assembly 15, is provided with a fiatbottom face 18,

and the vertical dimension as seen in Figure l, of the respective endsof the pin is such as to fit into and slidably engage the edges ofrespective slots 19, provided in the remaining corresponding extremitiesof the brake arm assembly 3.

As will be seen by reference to both Figure l and Figure 2, leverassembly 15, comprises a pair of spaced, parallel straight bars, 15a and15b, of rectangular cross section, for reasons of structural simplicity.In view of this, provision is made through respective holes 21 and 22 inthis lever assembly to clear the brake arm pivot pins 4 and 6. Thus itwill be appreciated that angular movement of lever assembly 15 isobtainable within the limits imposed by the clearance of the respectiveholes 21 and 22 about the respective pivot pins 4 and 6.

Since it is desirable in operation of the brake to minimize conditionsof back lash due to lost motion in certain of the connections, a spring23 is connected between pins 24 and 25, respectively mounted on leverassembly 15, and brake arm assembly 3. This spring is under tension andconsequently tends to move the pins 24 and 25 together. In so doing thebrake arm assembly 3 is biased counterclockwise, as viewed in Figure l,to a position in which the bottom edge of slot 19, abuts the fiat face18 on the bottom side of pin 17. Also cross piece or trunnion pin 27whose ends are carried by lever assembly 15 is biased upwardly, as willbe explained hereinafter.

A frictional connection is provided between the lever assembly 15 andbrake arm assembly 2, for the purpose .of providing an adjustableconnection of lever assembly 15 with brake arm assembly 2 through whichlimited torque may be applied to actuate the brake arm assembly 2 in adirection to release the brake shoe 9 from the wheel, but which yetprovides for relative angular movement between the lever assembly 1.5and brake arm assembly 2, when the lever assembly is movedcounterclockwise, as viewed in Figure l, to apply the brake shoe to thewheel. This frictional connection comprises a pair of friction washersor plate 2Q, which are respectively disposed between the adjacent leversof the brake arm assembly 2 and tie lever assembly 15, and furthercomprise a pair of spring washers 20a, disposed between the adjacentfaces of levers 15a, and 15b. A compression spring 201; disposed.between these spring washers thrusts the levers 15a and 15b apart asseen in Figure 2 and securely engages the respective levers with therespective friction plates or washers 20.

With the construction thus far described, if a downward force is exertedon the left hand end of lever assembly 15, the lever assembly will tendto pivot about the center of shaft 4 due to the friction device justdescribed and will move in a counterclockwise direction as viewed inFigure 1. Pin 17 will therefore tend to move downwardly and pin 16 willtend to move upwardly. These forces cause the respective brake armassemblies to rotate about their respective pivot pins 4 and 6, brakearm assembly 2 rotating counterclockwise and brake arm assembly 3rotating clockwise, to apply the respective shoes to the brake wheel.Since the holes 21 and 22 in lever assembly 15 are provide, it will beappreciated that this small counterclockwise movement of the leverassembly will not be obstructed by the respective brake arm assemblypivot pins 4 and 6.

For a particular location of the wheel, for example, a location of thewheel exactly on the designed center line of the brake, as shown inFigure l, the lever assembly 15, at the time the brake shoes engage thebrake wheel, will occupy a given angular position with respect to therespec tive brake arms. However, if the brake wheel should be to theright or to the left of this particular position, the lever assembly 15would occupy a different angular position with respect to the brake armsthan that which is illustrated. Under these conditions the angularrelationship of the lever assembly 15 with respect to brake arm assembly2, must change in an amount dictated by the degree of misalignment andthis is physically possible since the braking force which is applied tothe left end of the lever assembly 15 is sufficient to overcome thefriction between lever assembly 15 and bralte arm assembly 2.

It will thus be appreciated that braking torque is applied to the brakearms through the connection of the lever system 15 to the respectivebrake arms at the two points 16 and 17. By proper selection of thevarious lever arms which are involved in this mechanical linka c, it ispossible to obtain equal braking torques as wall be shown hereinafter.

It is desirable, although not absolutely necessary in this instance,that any misalignment of the brake wheel with respect to the designedcenter line of the brake, resulting in angular displacement of the leverassembly 15, shall not result in vertical displacement of the left endof this lever assembly. In the applicants copcnding application SerialNo. 249,498, filed on the same date as this application and entitledBrake, if such vertical displacement occurs, due to such misalignment,the travel of the brake engaging and brake releasing mechanism ischanged to some new value. To offset such a change it would then benecessary to effect an adjustment of the brake mechanism to restore thetravel of the brake operating mechanism to its initial condition.

However, in the present brake such vertical displacement merely changesthe relative positions of certain components of the brake releasingmechanism, yet to be described and does not affect the travel of suchmechanism. Hence, in this instance such displacement will not disturbbrake releasing movement although calibration for a given braking torquemay be changed to a small extent.

The illustrated linkage system, however, is relatively proportioned insuch a manner that the left end of the lever assembly 15 does not moveeven though misalignment of the brake wheel with respect to the designedcenter line of the brake may exist.

This will be appreciated from a consideration of the respective leverarms for the condition in whch the brake wheel is moved to the left ofthe designed center line of the brake. Under this condition both brakearm assemblies will be rotated in a counterclockwise direction asviewed. Consequently, both pins 16 and 17 will move upwardly, and theratio of the movement of the pin 16 to the pin 17 will be proportionalto the ratio of the dimension y to the dimension 2:, illustrated in thedrawing. If this ratio is properly selected, the distance traveled byeach pin will correspond to the distance between the sides of an anglesubtended by the angular movement of the lever system 15, which anglehas its vertex at the left end of the lever system.

This might be realized as follows: When the lever assembly 15 is rotatedabout its left end, the pins 16 and 17 move an amount corresponding tothe ratio y to x of the respective moment arms y and x. Consequently, ifthe ratio of y to x is made equal to the ratio of y to x, any movementof the wheel to the right or to the left of the designed center linewill result in a rotation of lever assembly 15 about its left end, andthis left end which is the point at which the spring force is applied toobtain braking torque will remain stationary and the adjustment orcalibration of the brake will not be changed.

The brake is applied by applying a downward force to the left end of thelever assembly 15 along the line of action P. To release the brake withthe construction provided, an upward force is applied to this samepoint. Because of the friction produced by the spring pressure engagingthe respective levers of the lever assembly and the brake arm assemblywith friction plate 20, upward force on the left end of the leverassembly 15, rotating this lever assembly in a clockwise direction, willtend to move .the brake arm assembly 2 angularly, at the same time thebrake arm assembly 3 is moved angularly, in directions to lift the brakeshoes from the wheels. The releasing torque, which moves brake armassembly 2 away from the brake wheel is applied thereto through thementioned frictional connection between the lever assembly 15 and thebrake arm assembly 2. Since there is no restraining force on this brakearm assembly, other than bearing friction, for this direction ofmovement, it will be appreciated that a relatively small frictionalforce will be sulficient to accomplish this end.

The pin 17, as indicated by dimensions designated 2:, is disposed midwaybetween the respective brake arm pivot pins 4 and 6, and, inasmuch asrotation of the lever assembly 15 takes place about the axis of the pin4 during brake releasing movement, it will be appreciated that bothbrake shoes are moved, in the same amount, away from the brake wheel 8.

With the lever arrangement illustrated, a downward force such as P onthe left end of lever assembly 15 produces equal and opposite forces onthe brake shoes. Taking moments about the respective pins 16 and 17, thedownward force on pin 17 is equal to:

The clockwise torque on brake arm 3 is:

Py'x

The counterclockwisetorque on brake arm2 is:

Since as earlier described herein, the ratio of y to x was made equal tothe ratio of y to x, it will be appreciated that the product of theseinversely related ratios in the final expression, will be unity, whichindicates that the torques are equal.

The mechanism for moving lever assembly 15 in brake engaging and brakereleasing directions includes a spindle 26 which is pivotally secured atits bottom end to the left end of lever assembly 15 by means of atrunnion pin 27. Trunnion pin 27 straddles the distance between thelever sections 1511 and 15b and is provided with a hole therethrough,which is normal to the trunnion axis, through which the bottom threadedend of spindle 26 is fitted. Spindle 26 is secured against rotation inthe trunnion 27 by means of a pair of nuts 28 which are threadedthereon, and which clamp the trunnion therebetween.

The spindle extends upwardly through a central cylindrical opening 29 ina magnet housing 30. The magnet housing is comprised of an upper part 31and a lower part 32. These two sections are secured together on theirmating faces by means of bolts 33. This magnet housing is supported by apair of angle sections 34 which are bolted to the vertical flanges ofthe base angles 1 and form a platform across their horizontal flanges onwhich the lower part 32 of the magnet housing is seated and secured bybolts 35.

Spindle 26 is slidably fitted through an externally threaded bushing 36which is rotatably mounted in the central opening of a cover plate 37which is bolted across the top of the opening 29 in the magnet housing31. A pair of sleeves 38 and 39, respectively, are fitted over thespindle 26. Sleeve 38 abuts the upper trunnion nut 28 and sleeve 39abuts the top end of the sleeve 38. This assembly of sleeves is securedaxially of spindle 26 by means of a spring washer 40 which is fittedover the spindle 26 in abutting relation with the upper end of sleeve39.

Spring washer 40 is secured in its position axially of spindle 26 bymeans of a clamp 41 which clamps over a reduced diameter section ofspindle 26 and abuts the upper end of the spring washer 40. A secondspring washer 42 threads over the externally threaded portion of bushing36 and is drilled and tapped at one point adjacent its peripheral edgeto receive a short rod 43, the bottom end of which threads into thementioned threaded hole. The upper end of this rod projects through ahole 44 in cover plate 37.

Springs 45 and 46 are compressed between respective shoulders on springwashers 40 and 42. The compressive force thrusting the lower springwasher 40 downwardly, which by reason of its secure connection withrespect to the spindle 26, drives the spindle 26 downwardly. Thisdownward thrust of the spindle through trunnion pin 27 rotates leverassembly 15 in a counterclockwise direction as viewed in Figure 1,driving pin 17 downwardly and pin 16 upwardly. As previously described,this movement engages the respective brake shoes with brake wheel 8,

The force of engagement of the brake shoes with the brake wheel isadjustable by the threaded bushing 36. It will be recalled that bushing36 is rotatably mounted in the cover plate 37. The end of this bushingwhich projects through the cover plate is provided at 47 with fiatsurfaces to receive a wrench. Rotation of the bush ing through theapplication of a wrench thereto moves the upper spring washer 42 up anddown along the threaded portion of the bushing. By reason of theconnection of rod 43 with the cover plate through the hole 44, springwasher 42 is stationarily secured against rotation at the time thatbushing 36 is rotated. Consequently, the only direction of freedom ofthis spring washer is axially oi": the threaded bushing.

Movement of this bushing controls the degree of compression of springsand 46 and consequently, controls the braking torque. The amount ofbraking torque may be indicated by suitable marks along the rod 43arranged to indicate the value of torque when the respective marks areadjacent the upper edge of a dust seal 43 secured to the top cover 37about the rod 43. The indicated position corresponds to 100% brakingtorque.

Means for mechanically releasing the brake assembly is provided in a nut49, which threads over the upper end of spindle 26. By rotating this nutdownwardly along spindle 2d, the nut is brought into engagement with theupper end of bushing 36. Continued rotation of the nut in this directionthen pulls spindle 26 upwardly through the magnet housing and moves thelever assembly in a clockwise direction, which as previously described,moves the brake arm and brake shoes in a direction to release the shoesfrom the brake wheel.

As earlier noted in this discussion, this brake assembly isself-compensating for misalignment of the brake wheel with respect tothe designed center line of the brake and for wear of the brake lining.This is accomplished, in general, by an actuating means embodying alinkage which is normally disengaged from the spindle 26 and whichoccupies a position adjacent the path of movement of the spindle suchthat displacement of the spindle longitudinally of its axis, does notvary the spacing between the spindle and the actuating means. Theactuating means is designed upon operation thereof to engage the spindleduring a first portion of its stroke and thereafter during the remainingportion of the stroke to move the spindle upwardly as viewed, to actuatelever assembly in a clockwise direction to release the brake.

It will be appreciated that numerous mechanical expedicnts may beemployed to eflect this general function. The specifically illustratedmeans embodies a suitable linkage which is actuated by armature member51 of an clectromagnct. the coil 52 of which is disposed within theupper magnet housing 31. prises a bushing 53 having bearing supports 54and 55, which is slidably fitted over the sleeves 38 and 39 on spin- Asbest seen in Fig. 4, bearing supports 54 and 55 extend outwardly onopposite sides of bushing 53. Respective pawl levers 5s and 57 arepivotally mounted by means of pins 58 and 59 in respective bearingsupports 54 and 55. The pins are secured with respect to the pawl leversby means of headless set screws 60 which are secured by nuts 51.Diametrically opposite sides of the .le 2o.

armature 51 are pivotally connected to the ends of pawl levers 55 and 57by respective pins 62 and 63 which pass through respective bosses 64 and65 secured to the bottom side of the armature 51 at diametricallyopposite points.

As will be seen by reference to Fig. 1 and Fig. 4, the armature iscircular in plan form and is provided with a central opening 64 whichclears the linkage. A shim 66 having a central opening thereincorresponding in size to the opening 64 in the armature is fitted to thetop side of the armature. This shim is of non-magnetic material and isutilized to prevent the armature from sticking due to the residual fluxin the magnet core after the coil is deenergized.

Pawl levers 56 and 57 are provided with pawl or clutch seats 67 and 68respectively, upon which the pawl or clutch pieces 69 and 7d aresecured. This assembly is disposed above the bearing supports 54 and 55upon the pawl levers and projects upwardly through the opening 64- inthe armature. This is clearly seen in both Figs. 1 and 4.

Specifically the linkage com- The faces of the pawl or clutch pieces 69and 70 which engage the threaded sleeve 39 are of a configurationcorresponding to the surface configuration of sleeve 39 to assurepositive engagement therewith. In one embodiment the sleeve 39 isprovided with threads having a high pitch and the faces of the pawl orclutch pieces are correspondingly shaped to mesh therewith. Themechanism components, as illustrated, including the magnet and armature,occupy relative positions corresponding to an energized condition of theelectromagnct coil. In this position, as shown, the pawl or clutchpieces 69 and 70 are both engaged with the sleeve 39.

It will be appreciated from a study of the mechanism herein abovedescribed that the armature for the electromagnet is carried entirely onthe ends of the pawl levers. Thus, when the magnet is dcenergized thearmature is released from the magnet core. The force of the springs 5and 46 drives the spindle 26 downwardly carrying with it the bushing 53,the pawl lever system and the armature. The movement of bushing 53downwardly is arrested by a shoulder 71, which is formed on the bushingadjacent its lower end, which engages an adjustable stop 72 threadedinto the bottom of the lower magnet housing 32. The travel of thebushing between its upper and lower positions is controlled by thevertical position of the stop 72 and may be adjusted to any requiredvalue within the illustrated limits. It will be appreciated that suchadjustment controls the open gap position of the armature andthereafter, until further adjustment of the stop is made, this open gapdistance will remain constant.

When the downward travel of bushing 53 is stopped the weight of thearmature on the pawl levers 56 and 57 rotates these leverscounterclockwise and clockwise, respectively, as viewed in Fig. 1, untilsuch time as webs 73 and 74 on pawl levers 56 and 57 respectively abutthe opposite edges of shoulder 71 on the bushing 53. in this positionthe pawl or clutch pieces 69 and '70 are con,- pletely disengaged fromthe threaded sleeve 39. Consequently, the spindle 26 is released fromthe armature controlled pawl or clutch linkage and completes itsdownward travel under the applied force of the compression springs 45and 46.

The counterclockwise rotation of lever l5 which results from thismovement of the spindle rotates the respective brake arms and the brakeshoes in such directions as to engage the brake shoes with the brakewheel, the spring force being sufiifiicicnt to arrest the brake wheel'srotation for any load up to that of the maximum capacity of the brake.The downward movement of the spindle stops at that time when the torquesapplied to the brake arms by the spring force acting on lever assembly15 is balanced by the resisting torques of the brake arms due toengagement of the brake shoes with the brake wheel. For a giventhickness of brake lining, this point of equilibrium is the maximumdownward position which the spindle 26 will occupy.

As the brake shoe lining wears, the ends of the brake arms which carrythe brake shoes will move closer to the brake wheel. Due to theconnection of the lever assembly 15, with the respective pins 16 and 17on the brake arms, the lever assembly 15 is free to rotate further in acounterclockwise direction. As a consequence, the downward travel of thespindle increases as the brake lining wears. When the armature is in itsfull downward position, the spindle as previously described iscompletely disengaged therefrom and consequently there is no restraintof spindle movement other than due to brake shoe pressure on the brakewheel.

Thus, a relative displacement in the longitudinal position of thespindle with respect to the engaging faces of the pawl or clutch pieces69 and 70 occurs, but there is no change in the dimension between thefaces of the pawl or clutch pieces 69 and 70 and the surface of thethreaded bushing 39 engaged by these pieces. Thus with each stroke ofthe armature upwardly, assuming a certain degree of brake liningwearwith each application ofuthe brake, the pawl pieces 69 and 70 may engagethe bushing 39 at any point along the length thereof.

Throughout this operation it will be appreciated there is no change inthe travel of the armature. Duringthe first interval of armature travelthe pawl levers 56 and 57 are rotated clockwise and counterclockwiserespectively until the faces of the pawl or clutch pieces 69 and 7t)engage the threaded sleeve 39. Angular movement of the pawl levers thenstops and continued movement of the armature upwardly, due to itslinkage with the magnetic field of the electromagnet, then carries thespindle 26 and the levers connected thereto, upwardly to move the braketo its released position. y

It will now be appreciated that according to the structure of thisinvention means are provided whereby the force which releases the brakehas a definite path of travel and that the length of this path isconstant whether the brake linings are worn evenly or unevenly or.completely worn out or, whether the brake 'whe el has expanded fromheat or contracted from cold'.' The arrange ment is such through thespecial compensatingifeatures to provide equalized shoe clearance underall of the named conditions, Y

It will 'be appreciated that the force of the springs decreases withshoe lining wear and the spindle moves downwardly a greater distancewith each application of the brake. For that reason the two springs 45and 46 are utilized, one inside the other, the combined scale of whichis low enough so that thevariation in torque'ranges from high for newlinings to 5% low when the linings are fully worn, giving a totalvariation in torque of only 10% over the full life of the brake linings.

Suitable means may be provided for indicating the extent of brake liningwear. Such means may be visual and of the form of a scale (not shown)adjacent the spindle 26. Other means may involve a suitable electricaldevice actuated by the spindle at a predetermined point in downwardtravel of the spindle 26 or of lever assembly 15, which electricaldevice controls a suitable audible, visual, or both, signaling device.

Although but one mechanical arrangement embodying this invention hasbeen illustrated herein, itwill be appreciated that numerous otherexpedients, in the nature of mechanical equivalents, may be'employed toachieve the results herein accomplished. For example inconnection withthe brake releasing mechanism, the general require: ment therein is thatthe brake releasing clutch or pawl system be frictionally released fromthe brake control lever when the magnet is deenergized, and that'thereshall be substantially no relative movement with regard to spacing ofthe clutch parts as the clutch element connected: with the brake controllever moves to new positions with wear of the brake shoe lining. jAdditionally, the configuration of the clutch faces may be subjected toconsiderablejchange depending upon the axial load o n spindle 26 and thematerials from which the clutcltjelef ments are made. Under certainconditions, smooth clutch faces may be utilized with success. While manybrake's are designed for electric controlthere are none the less manyapplications where electric controlmay'j not be feasible and so othermeans such as hydraulic or manual force may be utilized to actuatethemechanism.

[It is therefore intended that this disclosure shall include such andother equivalent detail variations in the subject matter disclosedandthat such subject matter tog'e'ther. with the illustrations of the,drawings shall be con.- sidered only as illustrative, of theprinciplesflofithisingention-.'andnot in'terpretedjin' alimitingl'serisel" f 3 'Icl'aim as'my'i'm'rentioriz'v ,1 "T. .1'. A.brake for controlling rotative fmovenient of a brake Wheel, comprising,a pair of pivotally mounted b ak rms ab ake sh X 939? one, a 'hb a e -ana .t 9 engage, aid. disengage s b Wheel upon movement of: said rbralgcarms, a.b ra-l e actuating are .10 lever assembly comprising'a leverpivotally connected with each brake arm at a point on each brake armdisplaced from the point of pivoting of the respective brake arms, afriction connection between said lever and one brake arm permittingrelative angular movement therebetween in the presence of braking forceson said lever and preventing relative angular movement therebetween inthe presence of brake releasing forces on said lever, a part on saidlever assembly being connected with said lever and being disposed formovement along a predetermined path to actuate said lever, and movableactuating means disposed adjacent said path of movement of said part formovement between inoperative and operative positionsand having amovement responsive member disengaged with said part'when' said movableactuating means is in said inoperative position and engaging said partand movingsaid part along said path in response to mpve'ment'of's'aidactuating means from said inoperative position towardoperative, position.

21' A brake for 'controllingrotative movement of a brake Wheel,comprising, a brake wheel, a main support,

a pair of. brakearmspivotally mounted on said support, a brake shoepivotally mounted on each brake arm, and adapted to engage and disengagesaid brake wheel upon movement of said brake arms, a lever assemblycomprising a lever connected with each brake arm at respective pointsdisplaced from the pointof pivoting of the respective brakearms on thesupport, a friction connection between said lever and one brake armpermitting relative angular movement therebetween in the presence ofbraking forces on said lever and preventing relative angular movementtherebetween in the presence of brake releasing forces on' said lever,,a part on said lever assembly being connected withsaid lever and beingdisposed for movement. along a predetermined path to actuate said lever,movable actuating means mounted on said support for movement betweeninoperativeand operative positions, said actuating means comprising amovable member disposed, adjacentsaid path of movement of said part anddisengaging said part when said actuating means is in said inoperativeposition, said movable member being actuated by, said actuating meansupon movement thereof toward operative position and engaging said partand moving said'part along said path.

3. A brake'for controlling rotativemovement of a brake wheel, comprisinga main support, a pair of brake arms pivotally mounted on said mainsupport, a brake shoeipivotally mounted on each brakearm and adapted toengage and disengage the brake wheel upon movement 'of the respectivebrake arms, a leverjpivotally connected Witheachbrake arm at a point oneach brake arm which is displaced from'the point of pivoting of thebrake arm on the support, a friction connectionbetween said lever andone brake arm permitting relative angular movement therebetween'in" thepresence of braking forces on said lever. and preventingrelative'angul'ar movement therebetween in'the presence .of brakereleasing forces on said lever, a rod pivotally connected to said lever,guide means supporting said rod for axial movement at an angle to said..lever, an actuator disposed adjacent said rod and movablesubstantiallyparallel to the axis of said rod, and atrelativelyflmovable part on saidactuator normally disengage'dnfromlsaid rod and movable into engagementwithsaid rod upon-movement of said actuator to grip and move saidrodwith said actuator.

-4. A bralre for controlling. rotative movement of a brakewheel,comprising. a main support, a pair of brake armspivotally mounted on.said main support, a brake shoe pivotally mountedv onleach brake armand adapted to engage anddisengage the brake wheel upon movement oftherespective brake'arms, .a lever. pivotally connected with eachbrake armat a pointon each brake arm which is displaced from the point ofpivoting of the brakelarm on the support, a. friction connection betweensaid lever and one, brake. arm permittingrelative angular movement '11therebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, an actuator support slidably fitted over said rod and a pawllever pivotally mounted on said actuator support and having a partthereon engageable with said rod upon the application of a force to saidpawl lever at a point thereon displaced from the point of pivotingthereof.

5. A brake for controlling rotative movement of a brake wheel,comprising. a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lover, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, an actuator support slidably fitted over said rod and a pawllever pivotally mounted on said actuator support and having a partthereon engageable with said rod, and a movable actuator pivotallyconnected with said pawl lever at a point thereon displaced from thepoint of pivoting of the pawl lever on said actuator support.

6. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, an actuator support slidably fitted over said rod and a pawllever pivotally mounted on said actuator support and having a partthereon engageable with said rod, and an electromagnet connected to saidpawl lever.

7. A brake for controlling rotative movement of a brake wheel.comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, a threaded section on said lever having a plurality ofthreads of high pitch thereon, an actuator disposed adjacent said rodand movable substantially parallel to the axis of said rod, a relativelymovable part on said actuator, said part having a face portion thereonof a configuration corresponding to the threads of said threadedsection, movement of said actuator in a given direction eiiectingmovement of said part in a direction to engage said face portion withsaid threaded section.

8. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, a threaded section on said lever having a plurality ofthreads of high pitch thereon, an actuator support slidably fitted oversaid rod, a pawl lever having a face portion thereon of a configurationcorresponding to the threads of said threaded section for engaging saidthreaded section, and actuating means connected with said pawl lever ata point displaced from the point of pivoting of the pawl lever on theactuator support.

9. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement there between in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, a threaded section on said lever having a plurality ofthreads of high pitch thereon, an actuator sup port slidably fitted oversaid rod, a pawl lever having a face portion thereon of a configurationcorresponding to the threads of said threaded section for engaging saidthreaded section, actuating means comprising an electromagnet mounted onsaid main support, and an armature for said electromagnet connected tosaid pawl lever,

10. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, a member slidably fitted over said rod and having respectivebearing supports on opposite sides thereof, a pawl lever pivotallymounted in each bearing support and each having a face portion adaptedto engage said rod upon angular movement of the respective pawl leversand a single actuating means connected with the pawl levers and movablebetween inoperative and operative positions, said actuating means insaid inoperative position disengaging said pawl levers from said rod andupon movement of said actuating means moving said pawl levers to engagesaid rod and carry said rod with said actuating means.

11. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mountedon each brake arm andadapted to engage and disengage the brake wheel upon move-- ment of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, a member slidably fitted over said rod and having respectivebearing supports on opposite sides thereof, a pawl lever pivotallymounted in each bearing support and each having a face portion adaptedto engage said rod upon angular movement of the respective pawl levers,an electromagnet mounted on said main support and an armature member forsaid electromagnet connected with each pawl lever to cause angularmovement thereof upon energization of said electromagnet. g

12. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of thebrake arm on the support, a friction connection betweensaid lever and one brake arm permitting relative angular movementtherebetween in the presence of braking forces on said lever andpreventing relative angular movement therebetween in the presence ofbrake releasing forces on said lever, a rod pivotally connected to saidlever, guide means supporting said rod for axial movement at an angle tosaid lever, a member slidably fitted over said rod and having respectivebearing supports on opposite sides thereof, a pawl lever pivotallymounted in each bearing support and each having a face portion adaptedto engage said rod upon angular movement of the respective pawl levers,an electromagnet disposed about said rod, an armature for saidelectromagnet, said armature having an opening therein for clearingsaid. rod and fitting about said rod in a position to be linked andmoved by the magnetic flux of the electromagnet, and means pivotallyconnecting said armature to each pawl lever at a point on each pawllever displaced from the axis of the respective bearing supports. I

13. A brake for controlling rotative movement ofa brake wheel,comprising a support, a pair of brake arms pivotally mounted at spacedpoints on said support, a brake shoe mounted'on-"eachbrake armand'adapted to engage and disengage said brake, wheel upon movement ofsaid brake arms, a lever assembly comprising a lever connected with eachbrake arm at a point on each brake arm displaced from the point ofpivoting of the respective brake arms, friction pivot means having apair of relatively slidable contiguous friction faces pivotally mountingsaid common lever on said support between the points of connection ofsaid lever with the respective brake arms, said friction pivot meansrestraining relative angular displacement between said lever and saidone brake arm throughout the range of brake releasing movement of saidone brake arm and permitting relative angular displacement between saidone brake arm and said lever in the presence of braking forces on saidlever when said shoes engage the brake wheel, a part of said leverassembly connected with said lever being movable along a predeterminedpath for moving said lever assembly, a movable actuating member disposedadjacent said part and being movable substantially along said path ofmovement between inoperative and operative positions, and

a pawl. lever-actuated by said movable actuating mentalong' said pathupon movement of said actuating member from said inoperative positiontowardsaidoperative position. I

14. A brake for controlling rotative movement of a brake wheel,comprising, a brake wheel, a main support, a pair of brake armspivotally mounted on said support, a brake shoepivotally mounted on eachbrake arm, and adapted to engage and disengage said brake wheel uponmovement of said brake arms, a lever assembly compris ing a leverconnected with each brake arm at respective points displaced from thepoint of pivoting of the respective brake arms on the support, fixedfriction pivot means on said support having a friction member slidablyfrictionally engaging said common lever at a point thereon between thepoints of connection of said lever with the respective brake arms, saidfriction pivotmeansfrestraining relative angular displacement'betweensaid lever'and said one brake arm throughout the range of brakereleasing movement of said onefbrake arm and permitting relative angulardisplacement between said one brake arm and said lever in the presenceof braking forces on said lever when said shoes engage the brake wheel,a part on said lever assembly connected with said lever being disposedfor movement along a predetermined path upon movement of said leverassembly, an actuating device movably mounted on said support formovement between inoperative and operative positions, said devicecomprising a movable pawl member disposed adjacent said part and beingdisengaged from said part when said actuating device is in saidinoperative position and'engaging said part and moving said part alongsaid path upon movement of said actuating device from said inoperativeposition toward said operative position.

15. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, fixed friction pivot means onsaid sup,- port having a friction member slidably. frictionally engagingsaid lever at a point thereon between the points of pivoting of saidlever with the respective brake arms, said friction pivot meansrestrainingrelative angular displacement between said lever and said onebrake arm throughout the range of brake releasing movement of said onebrake arm'and permiting relative angular dis placement'between said onebrake arm andsaid lever in the presence of braking'forces on said leverwhen said shoes engage the brake wheel, a rod pivotally connected tosaid lever, guide means supporting said rod for axial movement at anangle to said lever, an actuator disposed adjacent said rod and movablesubstantially parallel to the axis of said rod between inoperative andoperative positions, and a relatively movable part on said actuatordisengaged from said rod when said actuator is in said inoperativeposition and movable into engagement with said rod upon movement of saidactuator toward said operative position to grip and move said rod withsaid actuator.

16. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, fixed friction pivot means onsaid support having afriction member slidably frictionally engaging saidlever at a point thereon between the points of pivoting of said leverwith the respective brake arms, said friction pivot means restrainingrelative angular displacement between said lever and said one brake armthroughout the range of brake releasing movement of said one brake armand permitting relative angular displacement between said one brake armand said lever in the presence of braking forces on said lever when saidshoes engage the brake wheel, a rod pivotally connected to said lever,guide means supporting said rod for axial movement at an angle to saidlever, an actuator support slidably fitted over said rod and a pawllever pivotally mounted on said actuator support and having a partthereon engageable with said rod upon the application of a force to saidpawl lever at a point thereon displaced from the point of pivotingthereof.

17. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, fixed friction pivot means onsaid support having a friction member slidably frictionally engagingsaid lever at a point thereon between the points of pivoting of saidlever with the respective brake arms, said friction pivot meansrestraining relative angular displacement between said lever and saidone brake arm throughout the range of brake releasing movement of saidone brake arm and permitting relative angular displacement between saidone brake arm and said lever in the presence of braking forces on saidlever when said shoes engage the brake wheel, a rod pivotally connectedto said lever, guide means supporting said rod for axial movement at anangle to said lever, a threaded section on said lever having a pluralityof threads of high pitch thereon, an actuator disposed adjacent said rodand movable substantially parallel to the axis of said rod betweeninoperative and operative positions, a relatively movable part on saidactuator actuated by movement of said actuator, said part having a faceportion thereon of a configuration corresponding to the threads of saidthreaded section and being positioned with said face portion disengagedfrom said threaded section when said actuator is in said inoperativeposition, movement of said actuator toward said operative positionactuating said relatively movable part in a direction toengage said faceportion with said threaded section.

18. A brake for controlling rotative movement of a brake Wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and, disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, fixed friction pivot means onsaid support having a friction member slidably frictionally engagingsaid lever at a point thereon between the points of pivoting of saidlever with the respective brake arms, said friction pivot meansrestraining relative angular displacement between said lever and saidone brake arm throughout the range of brake releasing movement of saidone brake arm and permitting relative angular displacement between saidone brake arm and said lever in the presence of breaking forces on saidlever when said shoes engage the brake wheel, a rod pivotally connectedto said lever, guide means supporting said rod for axial movement at anangle to said lever, a member slidably fitted over said rod and havingrespective bearing supports on opposite sides thereof, a pawl leverpivotally mounted in each bearing support and each having a face portionadapted to engage said rod upon angular movement of the respective pawllevers and a single actuating means connected with the pawl levers.

19. A brake for controlling rotative movement of a brake wheel,comprising a main support, a pair of brake arms pivotally mounted onsaid main support, a brake shoe pivotally mounted on each brake arm andadapted to engage and disengage the brake wheel upon movement of therespective brake arms, a lever pivotally connected with each brake armat a point on each brake arm which is displaced from the point ofpivoting of the brake arm on the support, fixed friction pivot means onsaid support having a friction member slidably frictionally engagingsaid lever at a point thereon between the points of pivoting of saidlever with the respective brake arms, said friction pivot meansrestraining relative angular displacement between said lever and saidone brake arm throughout the range of brake releasing movement of saidone brake arm and permitting relative angular displacement between saidone brake arm and said lever in the presence of breaking forces on saidlever when said shoes engage the brake wheel, a rod pivotally connectedto said lever, guide means supporting said rod for axial movement at anangle to said lever, a member slidably fitted over said rod and havingrespective hearing supports on opposite sides thereof, a pawl leverpivotally mounted in each bearing support and each having a face portionadapted to engage said rod upon angular movement of the respective pawllevers, an electromagnet disposed about said rod, an armature for saidelectromagnet, said armature having an opening therein for clearing saidrod and fitting about said rod in a position to be linked and moved bythe magnetic flux of the electromagnet, and means pivotally connectingsaid armature to each pawl lever at a point on each pawl lever displacedfrom the axis of the respective bearing supports.

References Cited in the file of this patent UNITED STATES PATENTS951,146 Paris Mar. 8, 1910 2,358,999 Ray Sept. 26, 1944 2,514,378 CurrieJuly 11, 1950 2,582,351 Olson Jan. 15, 1952

